Gas pumping methods and apparatus



M h 8, 1966 c. H. NAUNDORF, JR

GAS PUMPING METHODS AND APPARATUS Filed July 10, 1963 United StatesPatent 3,239,134 GAS PUMPING METHODS AND APPAEATUS Charles H. Naundorf,Era, Rochester, N.Y., assignor to Consolidated Vacuum Corporation,Rochester, NJiL, a corporation of New York Filed July it 1963, Ser. No.294,078 7 Claims. (Cl. 2343-1) The present invention relates to gaspumping methods and apparatus and, more particularly, to methods andapparatus for moving or evacuating gas molecules from a space by meansof an electric arc plasma.

The subject invention provides improved methods and apparatus for movingor evacuating gas molecules from a space without objectionablecontamination of the space or the gas.

According to the invention a nozzle is prepared which has a tlu oatregion and a divergent portion adjacent the throat region. The throatregion is placed into communication with the space to be evacuated. Anelectric arc plasma is established in the throat region whereby gasmolecules are drawn from the space to be evacuated through the throatregion and are expelled through the divergent portion of the nozzle. Thegas thus drawn from the space to be evacuated will be heated by theelectric arc plasma as it passes through the throat region. In thedivergent nozzle portion, this heated gas will expand and thus help toreduce the pressure at the nozzle throat. In this manner, the efiiciencyof the pumping operation is greatly increased.

If desired, a negatively biased, apertured screen may be placed adjacentthe open end of the divergent nozzle portion to accelerate the gas ionsemerging from the arc plasma and thus further reduce the pressure at thenozzle throat and increase the efiiciency of the pumping operation.

A further increase in pumping efliciency is experienced if the nozzle ismade to be of the convergent-divergent type, with the convergent nozzleportion being exposed to the space to be evacuated. A larger amount ofgas molecules will then be advanced to the arc plasma during operationof the pump.

A large increase in pumping eificiency is also obtained by supplying thearc plasma with an ionizable gas, such as nitrogen, argon and the like,during the pumping operation. This gas is ionized and heated in the areplasma and leaves the nozzle through its divergent portion, therebyreducing the pressure at the nozzle throat.

The are plasma is preferably established by striking an electric arc inthe throat region of the nozzle. To this end, the throat region may bemade of electroconductive material and an electrode may be providedadjacent the throat region. The throat region is then preferablyconnected to the positive terminal of a direct-current source and theelectrode to the negative terminal of this source. An arc is then struckbetween electrode and nozzle throat. The electrons traveling in this arefrom the cathode to the anode, that is from the electrode to the innerwall of the throat region, will entrain the gas molecules present in theregion of the electric arc. In this manner, gas molecules arecontinuously removed from the space to be evacuated, inasmuch as theelectrons in the arc travel at high velocity and occur in great number.

It will now be appreciated that the method of the invention has utilitynot only for evacuating spaces or vessels, but also for moving gasses ina predetermined direction. Thus, the expressions evacuated or space tobe evacuated as used herein should be understood as referring not onlyto high vacuum evacuation processes, but also to gas pumping operationsin general where the object is to move a gas in a predetermineddirection.

The apparatus of the invention comprises a nozzle having a throat regionadapted to communicate with the space to be evacuated and including adivergent portion communicating with the throat region. The apparatus ofthe invention includes means for establishing an electric arc plasma inthe throat region to draw gas molecules from the space to be evacuatedthrough the throat region and cause the gas molecules to be expelledthrough the divergent portion.

The throat region may comprise electroconductive material and the meansfor establishing the arc plasma may include an electrode locatedadjacent the throat region. Preferably, a direct-current source may beconnected with its positive terminal to the throat region and with itsnegative terminal to the electrode. The direct-current source isdimensioned to maintain an electric are between the electrode and thethroat region, with the electrode serving as a cathode and the throatregion as an anode for the electric arc.

The electrode may have a hollow cylindrical configuration and anionizable pumping gas may be supplied to the electric are through thehollow electrode. The ionizable pumping gas may, however, also besupplied to the electric are by means of nozzles arranged in the spacebetween the electrode and the nozzle throat region.

The apparatus of the invention may include an apertured screen locatedadjacent the open end of the divergent nozzles portion. This screen maybe negatively biased with respect to the nozzle, so that ionized gasmolecules are accelerated from within the divergent nozzle portiontowards the open end thereof. The gas molecules thus accelerated aresubstantially neutralized at the screen and leave the apparatus throughthe apertures in the screen.

The invention and its operation and utility will become more readilyapparent from the following detailed description of preferredembodiments thereof, illustrated by way of example in the accompanyingdrawings, in which:

FIG. 1 shows diagrammatically and partially in section a vacuum pumpaccording to the invention;

FIG. 2 shows a first modification of the apparatus illustrated in FIG.1; and

FIG. 3 shows a detail, partially in section, of a second modification ofthe apparatus of FIG. 1 or a modification of the apparatus of FIG. 2.

The object of the vacuum pump 10 illustrated in FIG. 1 is to pump gas orgas molecules from a region 14 to a region 15. A wall 16 has beenschematically illustrated between regions 14 and 15 to indicate thatthese two regions are separated and isolated from each other. Inpractice, the region 14 may be the inside of a vessel to be evacuated,or of a chamber connected to a vessel to be evacuated, and the region 15may be a chamber that is pre-evacuated by any suitable conventionalmeans, such as mechanical, oil difiusion or mercury pumps (not shown).

The vacuum pump 10 comprises a nozzle 18 having a throat region 19 and adivergent portion 20. The divergent portion 20 communicates with thethroat region 19 and has a discharge opening 21. The nozzle 13 also hasa convergent portion 22 which, in the instant embodiment, is integralwith the throat region 19. In brief, the nozzle 2% is of theconvergent-divergent type. In addition, the nozzle 28* has a symmetricalconfiguration about longitudinal axis 25.

An electrode 26 is located on axis 25 and in the vicinity of the throatregion 19. Nozzle 20 is of electroconductive material and has thepositive terminal of a directcurrent source 27 connected thereto. Thenegative terminal of source 27 is connected to electrode '26. Whilesource 27 has been illustrated in the general area of electrode 26 andconvergent portion 22, it will of course be J! understood that thesource 27, in practice, will be located outside region 14, as well asregion 15.

Source 27 is constructed and dimensioned to strike and maintain an are30 between electrode 26 and nozzle region 19. To this effect, the source27 may include a high voltage source for striking an arc and a lowvoltage source (not shown in detail) for maintaining the are 30. Thislow voltage source, which is connected to electrode 26 and nozzle 18 aslong as the are 30 is to be maintained, may, for example, h ve a voltageof some 50 to 500 volts and a nominal current rating of some 100 to 300amperes. During the existence of are 30, electrons will it w fromelectrode or cathode 25 to throat region or anode 19 and part ofconvergent portion 22, as has been schematically indicated in thedrawings by means of arrows 32.

Electrode 26 is of the non-consumable type to prevent unduecontamination of the regions 14 and and of the gas being pumped. Forexample, electrode may be a tungsten electrode or may be of another oneof the conventional high-temperature and consumption resistant electrodematerials. The nozzle 18 may, for example, be of stainless steel orother suitable consumption resistant material. The apparatus 1% includesa cooling jacket which encompasses the throat region 19. The coolingjacket 35 has an inlet 36 and an outlet 37 for admission and withdrawalof a suitable cooling medium 33, such as water, to and from the coolingjacket 35. This cooling jacket 25 serves to maintain the nozzle 13 atthroat region 19 at reasonable temperatures. If desired, heat-conductingelements (not shown) may be provided between nozzle 18 and jacket 35 orthe jacket 35 may be disposed in close proximity to or in contact withnozzle 18 to accomplish a desired cooling effect.

The electrons in the are 34 will flow in great numbers and at greatvelocity fronrelectt'ode 26 to the wall of nozzle throat region 19 andwill thus entrain gas molecules present in throat region 19. Thesemolecules will be ionized as schematically indicated at 4d, and willthus be driven through convergent nozzle portion 26, as indicated at4-1, and the opening 21 thereof. In this manner, gas molecules will bedrawn from region 14 and moved to region 15. The electrons travelingwithin throat region 19 form a dense sheath which prevents backfiow ormigration of pumped gas molecules into t e region 14.

It will now be appreciated that FIG. 1 shows an apparatus for evacuatinga space in an efiicient and advantageous manner. If desired, thisapparatus could also be employed for moving or transferring gasses in acirculation or pumping system.

FIGS. 2 and 3 shows apparatus similar to that of FIG. 1, so that likereference numerals have been employed for like elements.

In the apparatus of FIG. 2, a hollow cylindrical electrode 26' with alongitudinal bore is employed in the place of electrode 26 shown inFIG. 1. During operation of the apparatus an ionizable gas 51, such asnitrogen, argon or the like, is supplied through bore 58 to the arcplasma or are 3t To this effect, a gas transfer chamber 53 is connectedto the electrode 26 so as to be in communication with bore 59. Gas issupplied to transfer chamber 53 by a conduit 55 which is connected to asuitable supply of pressurized gas 55, such as a steel bottle locatedoutside regions 14 and 15. In this manner, the ionizable gas 14 will besupplied to the are 36' without entering the low-pressure region 14.This gas will be entrained and ionized by the electrons in are 39 alongwith the gas molecules pumped from region 14. Subsequently, this gaswill also pass through and expand in divergent portion 20 and will thussignificantly increase the aspiration of gas molecules from region 14.If desired, a pump (not shown) may be associated with gas supply as forrecovery of ionizable gas from region 15 and re-use thereof in are 30.

In the apparatus of FIG. 3, a screen 60 with apertures 61 is located infront of opening 21 of divergent nozzle portion 28. The remainingstructure of the apparatus of FIG. 3 may be the same as that shown inFIG. 1 or in FiG. 2, so that only the larger end of divergent nozzleportion 26, a high-voltage source 62, and the screen 69 with apertures61 have been illustrated in FIG. 3. The screen may be a metal sheet witha largenumber of apertures or may also consist of wire mesh. Theapertured or perforated screen 60 is baised negatively with respect tonozzle 13 by means of the high-voltage source 62 which is connected toscreen and nozzle 18 as shown and which, in ractice, is preferablylocated outside region 15. Screen 6% is effective to accelerate the gasmolecules within divergent portion 28 towards the opening 21. At screen69, the gas molecules are neutralized and pass through the apertures5-9. In this manner, the aspiration of gas molecules from region 16 isfurther increased. if desired, the gas supply structure of FIG. 2 may becombined with the screen structure of FIG. 3 to realize maximum pumpingefficiency.

While an arcing electrode structure has been shown in the drawings,convention or other types ofi plasmaproducing means could be employed inits place. Various other modifications will be apparent to those skilledin the art.

I claim:

1. Apparatus for evaluating gas molecules from a chamber, comprising anozzle having a throat region connected to said chamber, and including adivergent electrically conductive nozzle portion connected to the throatregion, and means for establishing a continuous electric arc plasma inthe throat region to draw gas molecules from said chamber through thethroat region and expel the gas molecules through the divergent portion.

2. Apparatus for evacuating gas molecules from a chamber, comprising anozzle having an electroconductive throat region connected to saidchamber, and including a divergent electrically conductive nozzleportion communicating with the throat region, an electrode located atthe throat region, and means for establishing a continuous electric arebetween the electrode and the throat reg-ion and maintaining a flow ofelectrons from the electrode to the throat region.

3. Apparatus for evacuating gas molecules from a space, comprising aconvergent-divergent nozzle having a symmetrical configuration withrespect to a longitudinal axis through the nozzle and being connected tosaid chamber, an electrode located on said axis and projecting into theconvergent portion of the nozzle, and means for establishing acontinuous electric are between the electrode and the nozzle andmaintaining a flow of electrons in said are from the electrode to thenozzle.

4. Apparatus for evacuating gas molecules from a chamber, comprising anozzle having an electroconductive throat region connected to saidchamber, and including a divergent portion connected to the throatregion, an electrode located at the throat region, means forestablishing a continuous electric are between the electrode and thethroat region and maintaining a flow of electrons from the electrode tothe throat region, and means for introducing ionizable gas into theelectric arc.

5. Apparatus for evacuating gas molecules from a chamber, comprising aconvergent-divergent nozzle having a symmetrical configuration withrespect to a longitudinal axis through the nozzle and being connected tosaid chamber, a hollow cylindrical electrode located on said axisadjacent the convergent portion of the nozzle, means for establishing acontinuous electric are between the electrode and the nozzle, and meansfor supplying ionizable gas through the hollow cylindrical electrode andinto said arc.

6. Apparatus for evacuating gas molecules from a chamber, comprising anozzle having a throat region connected to said chamber, and includingan electrically conductive divergent nozzle portion connected to thethroat region, means for establishing an electric arc plasma in thethroat region to draw gas molecules from said chamber through the throatregion and expel the gas molecules through the divergent portion, anapertured screen adjacent said divergent nozzle portion, and means forelectrically biasing said screen with respect to said divergent nozzleportion to accelerate gas molecules from said divergent nozzle portionto said screen and through the apertures thereof.

7. Apparatus for evacuating gas molecules from a chamber, comprising anozzle having an electrically conductive throat region connected to saidchamber, and including an electrically conductive divergent portionconnected to the throat region, an electrode located at the throatregion, means for establishing an electric are between the electrode andthe throat region and maintaining a flow of electrons from theelect-rode to the throat region, means for introducing ionizable gasinto the electric are, an apertured screen adjacent said divergentportion, and means for electrically biasing said screen with respect tosaid divergent nozzle portion to accelerate gas molecules from saiddivergent portion to said screen and through the apertures thereof.

References Cited by the Examiner UNITED STATES PATENTS 2,279,586 4/ 1942Bennett 23069 2,327,588 8/1943 Bennett 23069 2,182,751 12/ 1939Reitherman 23069 2,765,975 10/ 1956 Lindenblad 23069 2,798,181 7/1957Foster 23069 2,809,314 10/1957 Herb 1031 2,862,099 11/1958 Gage.

3,041,824- 7/ 1962 Berhman -35.5 3,077,108 2/1963 Gage et al 10313,081,020 3/1963 Rostas 230-60 3,091,079 5/1963 Kunen 60-355 FOREIGNPATENTS 1,246,669 10/ 1960 France.

OTHER REFERENCES Discovery, page 16 (FIG. 2), July 1963.

LAURENCE V. EFNER, Primary Examiner.

1. APPARATUS FOR EVALUATING GAS MOLECULES FROM A CHAMBER, COMPRISING ANOZZLE HAVING A THROAT REGION CONNECTED TO SAID CHAMBER, AND INCLUDING ADIVERGENT ELECTRICALLY CONDUCTIVE NOZZLE PORTION CONNECTED TO THE THROATREGION, AND MEANS FOR ESTABLISHING A CONTINUOUS ELECTRIC ARC PLASMA INTHE THROAT REGION TO DRAW GAS MOLECULES FROM SAID CHAMBER THROUGH THETHROAT REGION AND EXPEL THE GAS MOLECULES THROUGH THE DIVERGENT PORTION.